The invention concerns a diaphragm pump with a crank drive having a connecting rod and an elastic diaphragm connected to the connecting rod, which diaphragm has an undercut fastening opening on its back side facing away from the compression chamber for inserting the complementarily formed attachment end of the connecting rod, wherein the connecting rod has a support surface on its attachment end for underside support of the central diaphragm area having a bearing surface, and wherein at least one fastening projection projecting in the axial direction of the connecting rod is provided on the support surface of the connecting rod for form-locking engagement in a central diaphragm area having at least one fastening opening.
Diaphragm pumps are also used, for example, as microdiaphragm pumps in connection with portable analysis devices. Since these analysis devices and their microdiaphragm pumps are usually operated independently of the power network by batteries or storage cells, motors with a low current consumption are necessary for this. Such motors have, however, only a limited performance capacity, for which reason the flexing work of the diaphragm should be reduced during operation of these previously known diaphragm pumps. With weak motors of this type the diaphragm must therefore also be configured sufficiently thin, but should--especially in connection with analysis devices--nevertheless be very tight, in order not to impair the accuracy of these devices.
Microdiaphragm pumps are already known, whose diaphragm is held between a metal thrust washer facing the compression chamber and the connecting rod head, wherein the thrust washer is attached to the connecting rod head by means of a screw connection, which passes through a central fastening opening in the diaphragm. Such a thrust washer clamp has, however, a central inelastic area of the diaphragm as a consequence, whereby the stroke volume is reduced, and the output of the previously known microdiaphragm pump is restricted.
One has thus also created a microdiaphragm pump, in which the diaphragm with its peripheral edge area clamped in the pump head form-lockingly encloses a connecting rod head with an approximately T-shaped cross section. Through this form-locking connection of the diaphragm on the connecting rod head, the previously mentioned thrust washer clamping of the diaphragm can be dispensed with. This previously known microdiaphragm pump has a greater stroke volume, since the diaphragm is also elastic in its central area. During operation of the previously known microdiaphragm pump, the diaphragm moves back and forth on the connecting rod head surrounded by it, which is associated with an additional flexing work activity of the diaphragm.
From DE 33 11 104 A1 a diaphragm pump of the type mentioned at the beginning is already known, whose diaphragm has an undercut fastening opening on the diaphragm underside facing away from the compression chamber. This fastening opening is connected with the complementarily formed attachment end of a connecting rod. On the attachment end of the connecting rod a fastening projection is provided for this, which is molded into the fastening opening. The fastening projection extends beyond a support surface situated on the attachment end of the connecting rod, which serves for underside support of a central diaphragm area having a bearing surface. Since the fastening projection is vulcanized into the diaphragm, and since the diaphragm of this previously known diaphragm pump has a central area increasingly thickened toward the center, the diaphragm, which is consequently flexibly configured only in its outer annular zone, can only be deformed with a correspondingly heavy flexing work. Such a diaphragm is therefore advantageously usable principally in larger diaphragm pumps with a high capacity pump drive, but less well suited for microdiaphragm pumps, whose motors have only a low performance capacity.